1. Technical Field
The present disclosure relates to a phosphor material which is combined with a light-emitting device such as a light-emitting diode (hereinafter referred to as “LED”) and a semiconductor laser diode (hereinafter referred to as “LD”) and which can be used in a light-emitting device such as a projector light source, a vehicle headlamp light source, and a white LED illumination light source. Furthermore, the present disclosure relates to a light-emitting device including the phosphor material.
2. Description of the Related Art
A illumination system including a white LED has higher efficiency and longer life as compared to a conventional illumination system and is widely used for business and home from the viewpoint of resource-saving and energy-saving.
In the most common white LED, a blue LED chip and a phosphor that absorbs a portion of blue light to emit yellow light are used and pseudo-white light is obtained by mixing blue light and yellow light, which is complementary thereto. However, the following LED is under development because color rendering properties, color reproducibility, and the like are required: a white LED including a combination of a blue LED chip, a green phosphor, and a red phosphor or a combination of a LED chip with a wavelength range from near-ultraviolet to blue-violet and three kinds of phosphors, that is, a blue phosphor, a green phosphor, and a red phosphor.
In applications, such as a projector light source and a vehicle headlamp light source, required to have high emission energy, a light source including a combination of an LD with a wavelength range from near-ultraviolet to blue-violet and a phosphor is under development.
A phosphor given by the compositional formula Ca2-2xLixEuxW2O8 or the like is known as a red phosphor which can be excited in a wavelength range from near-ultraviolet to blue and which has an Eu3+ luminescent center to emit light in the red region as disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 2007-254517, 2008-7644, and 2010-229388.
However, conventional red phosphors do not have sufficient luminous efficiency. Temperature characteristics thereof have not been taken into account. Therefore, there is a big problem in that the ambient temperature of a phosphor used is likely to rise particularly in a high emission energy region.